Pharmaceuticals, biological specimens and foodstuffs are among the most commonly freeze-dried ("lyophilized") materials. Though it would seem relatively easy to achieve desirable results, namely the dry state, by starting with an aqueous solution of a pharmaceutical, then freezing the solution and subliming the resulting ice, it is not. The purpose of freeze-drying is to minimize the changes in the properties of the substance while improving its stability at or near room temperature. Much has been published as to how to do this effectively (See, for example, Edwards Freeze-Drying Handbook, by Terence W. G. Rowe and John W. Snowman, published by Edwards High Vacuum, Crawley, England (1976). The problem is that in one or the other stages of freeze-drying, the material being freeze dried is undesirably altered.
A great deal of well-publicized effort has been directed to the freeze-drying of biological materials because of the criticality of the process steps required to obtain satisfactory results (see Freezing and Drying of Biological Materials, edited by O. St. Whitelock, "Annals of the New York Academy of Sciences", Vol 85, Art. 2, pgs 501-734, published by The Academy 1960). A comparable amount of less well-publicized effort has been directed to the freeze-drying of various pharmaceuticals for the twin purposes of maintaining their potency and stability over extended periods of time under ambient conditions, and to provide convenience in dispensing or using the pharmaceuticals.
Much attention has been paid, and much effort had been directed, neither too well-publicized, to the importance of presenting a pharmaceutically elegant dosage quantity of a pharmaceutical which must also maintain its potency and stability. In most instances, the freeze-dried pharmaceutical is deposited as a product (or "cake") which adheres to the sides of the vial or other container in which the precursor solution is freeze-dried. As the preferred form of packaging freeze-dried pharmaceuticals is in glass vials or containers, it will immediately be evident that a cake or plug tightly held in a glass container, near its bottom, has greater visual appeal than a loose powder, particularly if the powder has a proclivity to dust. When a pharmaceutical defies being successfully freeze-dried, that is, being reduced to a stable pharmaceutically elegant product without deleteriously affecting the physiological properties of the pharmaceutical, it is generally packaged as a dry powder.
This is precisely the packaging history of cyclophosphamide monohydrate and cyclophosphamide (either of which is referred to herein as "CPA" for brevity), which is a synthetic antineoplastic drug and immunosuppressive agent widely used for the treatment of a variety of malignant and non-malignant diseases. CPA is described in greater detail in U.S. Pat. No. 3,018,302 which is incorporated by reference thereto as if fully set forth herein, and also in the Merck Index, inter alia, the disclosures of which are similarly incorporated by reference.
The drug is currently packaged as a "dry" powder in vials into which dosage amounts of CPA in combination with sodium chloride are "powder filled". By "powder filled" I refer to the drug being measured into the vials in predetermined amounts as a mixture of powders. The water content of the powder in a dosage amount of powder filled CPA is in the range from 4.3-4.8 percent by weight (% by wt) based on the total weight of the powder in the vial. Just prior to use, the powder in the vials is reconstituted with Sterile Water for Injection, USP, or other suitable sterile solvents or diluents, and the reconstituted solution is administered to a patient.
However, the dissolution in water may not be readily accomplished, the time of solution for a 0.5 g dosage amount (which contains about 0.225 g NaCl solids) ranging from about 2 min (minutes) to about 2 hr (hours) or more, depending upon the particular physical/chemical characteristics of the CPA and NaCl in a particular batch of powder measured into a vial. A freeze-dried CPA product of this invention, however, is reconstituted by dissolving in water almost immediately, that is, in less than about 1 minute, and usually in less than 30 seconds. Speedy reconstitution is of great commercial significance because of the time saved by those responsible for administering the drug. The terms "dosage amount" and "product" are used herein to refer to the formulated and `finished` CPA as it is to be presented in a dosage unit form for sale in a vial.
The sodium chloride is used to improve flow characteristics as an aid to powder filling, but it also renders the resulting reconstituted product hypertonic, which is not necessarily desirable. Moreover, the powder so obtained is relatively difficult to meter accurately into vials (as compared with the filling of an aqueous solution). Also said powder is far more difficult to prepare in terms of achieving the highly desirable pharmaceutical characteristic of homogeneity. Product cryodessicated from a homogeneous solution is, by its very nature, of optimum uniformity.
Still another problem associated with "powder-filled" vials of CPA containing NaCl (referred to herein as "stabilized CPA") is that, in common with other powders, it is difficult to exclude extraneous contaminants, particularly minute fibers and the like, which somehow find their way even into filling rooms meeting clean room standards. As a practical matter, the operation of conventional powder-filling machinery in a filling room appears to preclude an atmosphere which is free from contaminant particles. Furthermore, the generation of airborne particles of CPA powder creates a potential health hazard to the operators since CPA powder itself is a potential carcinogen.
In pharmaceutical technology, it is highly unusual to encounter a drug which can be too dry. In most cases the drier the product the more stable it is, but in the case of CPA with or without an excipient, it is found to be essential to have sufficient moisture in the product to return to the hydrate form which is essential for stability. It is generally hypothesized that this stable hydrate form is the monohydrate, but not having established this hypothesis as a fact, the rehydrated CPA is referred to herein as "CPA hydrate". By "hydrate" I refer to a compound formed by the chemical combination of water (bound) to CPA in a definite molecular ratio.
It will now be evident why freeze drying an aqueous solution of CPA with or without an excipient, and adjusted for desirable tonicity, would be a preferred manner of marketing dosage amounts of stable CPA hydrate. However, CPA hydrate, whether by itself, or with an excipient, is known to defy freeze drying so as to retain to hydrate form which is critical for stability. Further, CPA hydrate, whether by itself, or with an excipient, is known to defy freeze drying so as to yield a pharmaceutically elegant product. By .-+.pharmaceutically elegant" I refer to a product which is visually pleasing, a criterion commonly used by those skilled in the art to gauge the market quality of the pharmaceutical. To be market quality, that is, marketable in conventional channels of the pharmaceutical trade, freeze dried CPA product must be both stable and pharmaceutically elegant.
In more qualitative terms such a pharmaceutically elegant product has a uniform appearance, and as examined from outside a glass vial or other container in which the product is held, is essentially free from bubbles or voids which individually do not exceed 2 mm in equivalent diameter ("equiv. diam."). The great difficulty associated with freeze drying a solution of CPA, whether alone, or with an excipient, is particularly noteworthy because combinations of numerous excipients, and many more drugs than excipients, are conventionally easily freeze-dried to produce elegant product.
Freeze-dried pharmaceuticals are highly preferred, because they are essentially free of particulate contaminants and are likely to have the sought-after pharmaceutical elegance. They are of better quality than equivalent powders, and can be dissolved in solvent just prior to use more easily than comparable powder filled pharmaceuticals.
The freeze drying method produces a product which is sterile and uncontaminated because it permits filtration of a solution of the desired product prior to filling. Such filtration is conventionally done through suitable microbiological filters. The procedure is far preferable to the techniques of powder filling. The filtered solution may then be precisely subdivided into suitable vials, and the vials then loaded into freeze-drying chambers where the solution is frozen and the ice sublimed under vacuum in a drying step, followed by a desorption step in which the moisture level is reduced to less than 3% by wt based on the weight of total solids, and preferably to less than 1.0% by wt.
The heretofore lack of success in freeze-drying CPA and producing an acceptable product, is particularly noteworthy because numerous drugs are routinely freeze dried to yield pharmaceutically elegant product. Drugs are often freeze-dried with sugars such as sucrose and lactose, and polyhydroxy alcohols (polyols) such as sorbitol and mannitol. For example, drugs freeze dried with mannitol include Platinol.RTM. (Bristol-Myers), DTIC-Dome (Miles), and Dantrium IV.RTM. (Norwich-Eaton), inter alia; those with sucrose, Palosein.RTM. (Diagnostic Data. Inc.), inter alia; those with lactose, Aclacinomycin (National Cancer Institute), inter alia.
Numerous attempts have been made to freeze dry CPA containing sodium chloride alone, but to date, the results have been unsatisfactory. Attempts have also been made to take advantage of the superior marketability of freeze-dried CPA containing an excipient in addition to NaCl, or without it, such excipient being chosen for desirable bulking, but to date, the results have also been unsatisfactory. The product with excipient, when dried to less than 7% by wt moisture, based on the total wt of product, is unsightly. By "unsightly" I refer to a cake in which there is flaking evidenced by plate-like flakes and granular odd-sized agglomerates.
When dried in a single stage, attempting to obtain a moisture content in the right amount for stability of the CPA product, by stopping the drying of the product in the vials loaded in the chamber, fails to provide a substantially uniform moisture content in all the vials. Though some vials may contain the right amount of moisture, the moisture content of the vials in the chamber is non-uniform and difficult to control utilizing conventional drying techniques. For example, a batch of 300 vials, each containing a 100 mg dosage amount of CPA and about 75 mg of mannitol as an excipient, when freeze dried to arrive at the desired moisture content (2 to 7% by wt based on the content of the vial), produced less than 100 vials which were in the desired moisture range. Moreover, the actual moisture content of individual acceptable vials varied widely within the range. As stated hereinabove, the moisture content of the CPA product is critical because outside the critical range, the product lacks the required stability of a marketable CPA product.
When too dry, that is, when the moisture bound to the CPA as water of hydration is substantially reduced, that is to less than 5.5% by wt on an excipient-free basis, and particularly when less than 3%, the product with no excipient in it melts at room temperature. Such melting also occurs when an excipient is present and the CPA product has less than 2% by wt moisture based on the wt of the product.
When the product is too wet, that is, when the moisture bound to the CPA as water of hydration is greater than 7% by wt, the product is both pharmaceutically inelegant and unstable. Such a high moisture content is present when the moisture content of the product, including excipient(s), is greater than 7% by wt based on the total wt of product.
Whether too dry, or too wet, the CPA product includes easily visible fissures wider than 2 mm, and/or large voids within the cake greater than 2 mm and generally even greater than 3 mm in equiv. diam. Bubbles, apparently caused by puffing during freeze drying, are also formed on the surface, at least some of which are greater than 2 mm in equiv. diam. Whether either voids or bubbles are present, or both, a dosage amount of CPA containing either is deemed unsuitable for the marketplace. It is realized that such suitability may vary particularly as applied to various countries in the world, but I use the term in relation to meeting the highest standards.
Though it is generally acknowledged that the visual appearance of adequately dry CPA product do not affect its pharmaceutical efficacy, purchasers and dispensers of pharmaceuticals expect freeze dried products to have pharmaceutical elegance which otherwise dried, powder filled CPA so conspicuously lacks, and they expect to get such elegance. Most of all, they expect to get it without sacrificing the stability of the drug.
In my numerous unsuccessful previous attempts directly to freeze-dry (that is, without a rehydration step) an aqueous solution of CPA containing at least an equivalent amount by weight ("equiv wt") of an excipient, and attempts to do so with a solution containing lesser amounts, with or without NaCl, caused ice to sublime so erratically that the result was a freeze-dried CPA product characterized by flaking, granulation, fissures, `blisters` or large bubbles referred to hereinabove, and random voids both large and small within the cake, so as to present a highly non-uniform, muddy, visually non-aesthetic appearance.
I am unaware of any disclosure relating to the freeze drying of a solution of CPA alone, or containing either NaCl or at least an equivalent weight of a sugar excipient, or both, intimately intermixed to produce a market quality, stable, freeze dried pharmaceutically elegant CPA product. By "stable" I refer to the ability of the CPA product to maintain, within specified (USP) limits of from 90% to 110% of the label potency of the freeze dried product after six months storage up until the date specified for its use, generally less than two years from the date of manufacture, at the recommended storage temperature (ambient, 20.degree.-25.degree. C.) when subjected to conditions defined in the USP procedure for high pressure liquid chromatographic ("HPLC") testing. The effectiveness of the drug is predicated upon its purity as active drug substance, that is, freedom from unacceptable degradation.
Except for the sugars disclosed herein, I found no other excipients which by themselves produced a market quality freeze dried CPA product. For the purposes herein, NaCl is not an excipient. Its presence in the freeze-dried CPA product is unnecessary. NaCl may be added in a minor amount by wt relative to the CPA (anhyd) to adjust the tonicity of the reconstituted CPA solution. The presence of a buffer salt is generally also unnecessary but a minor amount by wt relative to the CPA (anhyd) may be added to ensure that the pH of the reconstituted solution is in the desired range of from about 3.5 to about 5.5.
I have been unable to freeze-dry CPA monohydrate product without an excipient, with or without NaCl. Even disaccharides by themselves are not particularly desirable from the point of view of producing a pharmaceutically elegant product, because they can exhibit erratic lyophilization characteristics and may be reconstituted with difficulty for use as aqueous solutions. Polyols such as mannitol, galactitol and sorbitol are incorporated with difficulty into acceptably freeze-dried CPA product unless the mannitol is present in an equiv. wt, or, a major amount by wt of the sugars including polyols used as excipients, the equivalent or minor amount being anhydrous CPA. For the purpose herein, aldoses, ketoses and polyols used as excipients are collectively referred to herein as sugars.